diff --git a/README.md b/README.md
index 96d3ef8d..1023b5c9 100644
--- a/README.md
+++ b/README.md
@@ -344,6 +344,24 @@ end
 ```
 The blocks are run when local files are being scanned and uploaded
 
+##### Config Method `file_ext_to_mime_type_overrides`
+It's reported that `mime-types` 3.x returns `application/ecmascript` instead of `application/javascript`  
+Such change of mime type might cause some CDN to disable asset compression  
+So this gem has defined a default override for file ext `js` to be mapped to `application/javascript` by default
+
+To customize the overrides:
+```ruby
+AssetSync.configure do |config|
+  # Clear the default overrides
+  config.file_ext_to_mime_type_overrides.clear
+  
+  # Add/Edit overrides
+  # Will call `#to_s` for inputs
+  config.file_ext_to_mime_type_overrides.add(:js, :"application/x-javascript")
+end
+```
+The blocks are run when local files are being scanned and uploaded
+
 #### Fog (Required)
 * **fog\_provider**: your storage provider *AWS* (S3) or *Rackspace* (Cloud Files) or *Google* (Google Storage) or *AzureRM* (Azure Blob)
 * **fog\_directory**: your bucket name
diff --git a/asset_sync.gemspec b/asset_sync.gemspec
index 56c15bb6..f34a46c1 100644
--- a/asset_sync.gemspec
+++ b/asset_sync.gemspec
@@ -24,7 +24,8 @@ Gem::Specification.new do |s|
 
   s.add_development_dependency "rspec"
   s.add_development_dependency "bundler"
-  s.add_development_dependency "jeweler"
+
+  s.add_development_dependency('mime-types', ">= 3.0")
 
   s.add_development_dependency "fog-aws"
   s.add_development_dependency "fog-azure-rm"
diff --git a/lib/asset_sync/config.rb b/lib/asset_sync/config.rb
index 125e8e3d..719d151f 100644
--- a/lib/asset_sync/config.rb
+++ b/lib/asset_sync/config.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "active_model"
 require "erb"
 require "yaml"
@@ -268,6 +270,11 @@ def additional_local_file_paths
       end
     end
 
+    #@api
+    def file_ext_to_mime_type_overrides
+      @file_ext_to_mime_type_overrides ||= FileExtToMimeTypeOverrides.new
+    end
+
   private
 
     # This is a proc to get additional local files paths
@@ -277,5 +284,43 @@ def additional_local_file_paths
     def default_manifest_directory
       File.join(::Rails.public_path, assets_prefix)
     end
+
+
+    # @api private
+    class FileExtToMimeTypeOverrides
+      def initialize
+        # The default is to prevent new mime type `application/ecmascript` to be returned
+        # which disables compression on some CDNs
+        @overrides = {
+          "js" => "application/javascript",
+        }
+      end
+
+      # @api
+      def add(ext, mime_type)
+        # Symbol / Mime type object might be passed in
+        # But we want strings only
+        @overrides.store(
+          ext.to_s, mime_type.to_s,
+        )
+      end
+
+      # @api
+      def clear
+        @overrides = {}
+      end
+
+
+      # @api private
+      def key?(key)
+        @overrides.key?(key)
+      end
+
+      # @api private
+      def fetch(key)
+        @overrides.fetch(key)
+      end
+
+    end
   end
 end
diff --git a/lib/asset_sync/multi_mime.rb b/lib/asset_sync/multi_mime.rb
index eb73d392..6a01ee4e 100644
--- a/lib/asset_sync/multi_mime.rb
+++ b/lib/asset_sync/multi_mime.rb
@@ -4,6 +4,11 @@ module AssetSync
   class MultiMime
 
     def self.lookup(ext)
+      overrides =
+        ::AssetSync.config.file_ext_to_mime_type_overrides
+      if overrides.key?(ext)
+        return overrides.fetch(ext)
+      end
 
       if defined?(::MIME::Types)
         ::MIME::Types.type_for(ext).first
diff --git a/spec/unit/multi_mime_spec.rb b/spec/unit/multi_mime_spec.rb
index ccf16d76..3b7d2397 100644
--- a/spec/unit/multi_mime_spec.rb
+++ b/spec/unit/multi_mime_spec.rb
@@ -36,6 +36,8 @@
     $".grep(/mime\//).each do |file_path|
       $".delete(file_path)
     end
+
+    AssetSync.config = AssetSync::Config.new
   end
 
   after(:all) do
@@ -69,4 +71,49 @@
 
   end
 
+  describe "use of option file_ext_to_mime_type_overrides" do
+    before(:each) do
+      require 'mime/types'
+    end
+
+    context "with default value" do
+      it "should return default value set by gem" do
+        expect(
+          AssetSync::MultiMime.lookup("js").to_s,
+        ).to eq("application/javascript")
+      end
+    end
+    context "with empty value" do
+      before(:each) do
+        AssetSync.config = AssetSync::Config.new
+        AssetSync.configure do |config|
+          config.file_ext_to_mime_type_overrides.clear
+        end
+      end
+
+      it "should return value from mime-types gem" do
+        expect(
+          AssetSync::MultiMime.lookup("js").to_s,
+        ).to eq("application/ecmascript")
+      end
+    end
+    context "with custom value" do
+      before(:each) do
+        AssetSync.config = AssetSync::Config.new
+        AssetSync.configure do |config|
+          config.file_ext_to_mime_type_overrides.add(
+            :js,
+            :"application/x-javascript",
+          )
+        end
+      end
+
+      it "should return value from mime-types gem" do
+        expect(
+          AssetSync::MultiMime.lookup("js").to_s,
+        ).to eq("application/x-javascript")
+      end
+    end
+  end
+
 end